The present invention relates generally to a semiconductor laser module, a manufacturing method thereof and an optical amplifier using the semiconductor laser module, and more particularly to a semiconductor laser module employing a semiconductor laser device provided with two stripes from which two laser beams are emitted, a manufacturing method thereof and an optical amplifier.
With progresses in the optical communications based on a dense wavelength division multiplexing transmission system over the recent years, a higher output is increasingly demanded to a pumping light source used for the optical amplifier.
Further, a greater expectation is recently given to a Raman amplifier as an amplifier for amplifying the beams having a much broader band than by an erbium-doped optical amplifier that has hitherto been used as the optical amplifier. The Raman amplification may be defined as a method of amplifying the optical signals, which utilizes such a phenomenon that a gain occurs on the side of frequencies as low as 13 THz on the basis of a pumping beam wavelength due to the stimulated Raman scattering occurred when the pumping beams enter an optical fiber, and, when the signal beams having the wavelength range containing the gain described above are inputted to the optical fiber in the thus pumped (excited) state, these signal beams are amplified.
According to the Raman amplification, the signal beams are amplified in a state where a polarizing direction of the signal beams is coincident with a polarizing direction of the pumping beams, and it is therefore required that an influence by a deviation between polarizing planes of the signal beam and of the pumping beam be minimized. For attaining this, a degree of polarization (DOP) has hitherto been reduced by obviating the polarization of the pumping beam (which may be called depolarization).
What is known as a conventional semiconductor laser module used as a pumping light source or the like of an optical amplifier, is a semiconductor laser module in which two fluxes of laser beams are polarization-synthesized and thus outputted from an optical fiber.
For example, Japanese Patent Application Laid-open No. Sho 60-76707 discloses a semiconductor laser module including first and second semiconductor laser devices, a polarization rotating element, a polarizing element, and optical fiber and a lens. The first and second semiconductor laser devices having their optical axes and polarizing planes that are parallel to each other and also their exit edge surfaces substantially coincident with each other, are disposed on a heat sink and emit first and second laser beams, respectively. The polarization rotating element is disposed on a light path for the first laser beam emitted from the first semiconductor laser device, and sets the polarizing plane of the first laser beam at a right angle to the polarizing plane of the second laser beam by rotating the former polarizing plane by 90xc2x0. The polarizing element serves to converge the light paths for the first and second laser beams with the polarizing planes orthogonal to each other by a birefringence effect. The optical fiber serves to receive the laser beams emerging from the polarizing element and let the laser beams travel outside. The lens serves to lead the laser beams converged by the polarizing element to the optical fiber. According to this semiconductor laser module, the first and second semiconductor laser devices are packaged as a unit (this technology will hereinafter be called a prior art 1).
Further, Japanese Patent Application Laid-open No. 2000-31575 discloses a semiconductor laser module including a thermoelectric cooler, first and second semiconductor laser devices mounted on the electron cooling device, first and second condenser lenses each for converging first and second laser beams emitted from the first and second semiconductor laser devices, a polarization-synthesizing element for polarization-synthesizing the first and second laser beams, and an optical fiber for receiving the laser beams emerging from the polarization-synthesizing element and letting the laser beams travel outside. Moreover, each of the first and second semiconductor laser devices is constructed as an LD (laser diode) array in which the laser diodes are arrayed at a pitch between center portions of emission parts on the order of 500 xcexcm. Further, each of the first and second condenser lenses is configured as a lens array for converging the laser beams such as a spherical lens array, a Fresnel lens array and so on (this technology will hereinafter be called a prior art 2).
The prior art 1 has the configuration in which the laser beams from the semiconductor laser device are received directly by the polarization rotating element or the polarizing element. As recognized by the prior inventors, obtainment of a high optical coupling efficiency with the configuration of the prior art 1 therefore involves a geometrical design in which a space between the semiconductor laser device and the lens is set on the order of 300 to 500 xcexcm. In fact, however, it is highly difficult to dispose the polarization rotating element and the polarizing element between the semiconductor laser device and the lens. A wider space can be formed by increasing a size of the lens, however, there remains a problem in that a size of the package becomes several times as large as package used at the present, which leads to a scale-up of the semiconductor laser module.
On the other hand, the prior art 2 has the configuration that the condenser lenses are disposed corresponding to the two semiconductor laser devices and thereafter the laser beams are polarization-synthesized, and therefore obviates the problem of the space in the prior art 1.
In the configuration, and as recognized by the prior inventors however, each lens receives one beam emitted at a comparatively wide interval (the inter-emission-center pitch; 500 xcexcm) respectively, thereby obtaining the two laser beams parallel to each other. This configuration consequently brings about the scale-up of the semiconductor laser device with the result that a quantity of the semiconductor chips acquired from one sheet of wafer decreases, and is therefore unsuited to mass-production. If a space between the stripes of the semiconductor laser device is set to be narrow in order to obviate this problem, the lens needs downsizing, and the beams emerging from the respective stripes are hard to split from each other. It is therefore difficult to perform the succeeding polarizing synthesization and the light synthesization as well.
Further, it is required that the lens be positioned with respect to the laser beam emitted from the semiconductor laser device, and hence the problem arises herein that a manufacturing process becomes complicated, and the manufacturing is time-consuming. According to the prior art 2, the lens includes the use of a lens array (such as a spherical lens array or, a Fresnel lens array) that is normally unused in order to obviate the positioning difficulty. The prior art 2 therefore has such a problem that the manufacturing cost is high, and it takes much time to manufacture the lens array described above.
In contrast to the prior art, the embodiments of the present invention are for a semiconductor laser module, a manufacturing method thereof and an optical amplifier that are capable of obtaining a high optical coupling efficiency, attaining a down-size and a mass-production, and reducing both of a manufacturing time and a manufacturing cost.
The present invention provides a semiconductor laser module comprising:
a single semiconductor laser device having a first light emitting stripe and at least one other light emitting stripe which are aligned to respectively emit a first laser beam and at least one other laser beam through a one edge surface;
a first lens positioned so that the first laser beam and the at least one other laser beam emitted from the semiconductor laser device are incident therealong, the first lens configured to separate the first laser beam and the at least one other laser beam;
a beam synthesizing member including
a first input part on which the first laser beam is incident,
at least one other input part on which the at least one other laser beam is incident, and
an output part from which the first laser beam emerging from the first input part and the at least one other laser beam emerging from the at least one other input part are multiplexed and emitted as a multiplexed laser beam; and
an optical fiber positioned to receive the multiplexed laser beam therein.
The present invention also provides an optical amplifier using comprising:
a pump beam generator having a plurality of semiconductor laser modules emitting multiplexed laser beams, with each semiconductor laser module including
a single semiconductor laser device having a first light emitting stripe and at least one other light emitting stripe which are aligned to respectively emit a first laser beam and at least one other laser beam through a one edge surface;
a first lens positioned so that the first laser beam and the at least one other laser beam emitted from the semiconductor laser device are incident therealong, the first lens configured to separate the first laser beam and the at least one other laser beam;
a beam synthesizing member including
a first input part on which the first laser beam is incident,
at least one other input part on which the at least one other laser beam is incident, and
an output part from which the first laser beam emerging from the first input part and the at least one other laser beam emerging from the at least one other input part are multiplexed and emitted as a multiplexed laser beam;
an optical fiber positioned to receive the multiplexed laser beam therein; and
a wave division multiplexer coupler configured to synthesize the multiplexed laser beams emitted by the plurality of semiconductor laser modules.
The present invention also provides a semiconducting laser module, comprising:
means for producing a first laser beam and a second laser beam from a single semiconductor laser device;
means for separating the first laser beam and a second laser beam; and
means for multiplexing the first laser beam and the second laser beam into a multiplexed laser beam.
The present invention also provides a method for generating a multiplexed laser beam, comprising steps of
producing a first laser beam and a second laser beam from a single semiconductor laser device;
separating the first laser beam and a second laser beam; and
multiplexing the first laser beam and the second laser beam into a multiplexed laser beam.